1. Field of the Invention
The present invention relates to a flame-retardant silicone rubber composition. More particularly, this invention relates to a flame-retardant silicone rubber composition that is transparent.
2. Description of the Prior Art
A number of methods are already known for rendering silicone rubbers flame retardant. One approach comprises the compounding or admixture into a curable silicone rubber composition of a platinum compound and at least one additional flame retarding agent such as titanium oxide, zinc carbonate, manganese carbonate, cerium hydroxide, iron oxide and carbon black.
The use of a cerium-modified silica filler to impart heat stability and flame retardanoy to peroxide-cured silicone rubber is taught in P. Nauroth et al. U.S. Pat. No. 4,360,388, on Nov. 23, 1982.
Organosiloxane compositions containing a cerium salt of a fatty acid having from 6 to 12 carbon atoms and that cure by a platinum-catalyzed hydrosilation reaction to yield a heat resistant and flame retardant silicone rubber are described in Japanese Patent Publication No. 58253, published on Apr. 30, 1980.
The presence of prior art flame-retarding agents and typical reinforcing fillers renders a cured silicone rubber organosiloxane composition containing these ingredients opaque.
Transparent silicone rubber can be obtained by curing addition reaction-curable silicone rubber compositions prepared from at least one vinyl group-containing organopolysiloxane, at least one organohydrogenpolysiloxane, and a platinum compound as catalyst. While these compositions exhibit some flame retardancy, their flame-retardant performance nevertheless is relatively low.
The present inventors carried out extensive research directed to solving the foregoing problems, and discovered as a result that, through the admixture of specific compounds, the intrinsic transparency of silicone rubbers can be retained while their flame retardancy can at the same time be substantially improved. The present invention is based on the results of these efforts.